The laboratory Sheep Colony is an NIH animal resource providing varied age animals that meet specific year-round requirements of the Clinical Hematology Branch, Laboratory of Technical Development, Pulmonary Branch, and Surgery Branch, DIR, NHLBI; and the Laboratory of Biomedical Sciences, IRP, NICHHD. Maintenance regimens in use have resulted in successful year-round breeding and production of varied age sheep. Practices that have contributed to reduction of undesired seasonal variables include: (1) continuous prophylactic immunization of all age animal groups; (2) accurate pregnancy diagnosis during first trimester using Doppler ultrasound; (3) monitoring of animal health using various diagnostic laboratory techniques; and (4) many husbandry techniques unique to this colony. Such practices have been cost prohibitive in commercial sheep flocks that result in animals delivered for laboratory use.